Wielding handmade bamboo baskets and nylon nets, hundreds of people waded thigh-deep into a muddy lake in eastern Cambodia on Sunday for an annual fish-catching ceremony where only traditional tools are used.

The ceremony is held each year in eastern Tboung Khmum province after the crop harvest to commemorate the country's proud fishing history, said local chief Uch Yoeun.

The event -- held in Choam Korvean commune, about 250 kilometres (155 miles) from the capital Phnom Penh -- attracts hundreds of farmers from surrounding villages.

They carry weaved baskets of different shapes, eager to try their hand at trapping the freshwater catfish and snakehead fish in the muddy Boeung Kroam lake.

"It has been a tradition since our ancestors' time," Uch Yoeun told AFP, adding that only one rule applies in this mass fishing event.

"We only allow traditional fishing tools to be used."

Authorities guarded Boeung Kroam lake for more than a month before the event -- to prevent illegal fishing and ensure there would be enough to catch at Sunday's event.

It kicked off in the early morning with hundreds of villagers racing to the lake, sporting straw hats and traditional scarves to shield themselves from the blazing sun.

The mood was light-hearted and many opted to grill the morning's catch by the lake over a smoldering fire.

But for villagers who had attended the event for several years, the day's haul proved disappointing.

"Before, there were bigger fish," said Chin Khoung, 50. "Now the fish are small and there's less (of them)."

The Southeast Asian country, which boasts the mighty Mekong river and its many tributaries, is heavily reliant on fish as a major source of protein for its population.

About 40 percent of the population depend on fishing for their livelihoods.

But fish stocks have declined in recent years due to hydropower dams built upstream in Cambodia and neighbouring countries, and the increase of illegal fishing methods, said Om Savath, who heads the Fisheries Action Coalition Team (FACT), which promotes sustainable resource management.

Using techniques like electrocution, "they can catch a lot of fish in a short time, but it is disastrous in the long term," Savath said.

The fish-catching ceremony in Choam Krovean is important because it helps to "raise awareness in communities about the use of family methods in fishing," he said.